The first witness to give evidence in the trial was Michell Burger, a woman who lived next to the Silverwoods Estate where Pistorius shot his girlfriend on Valentine's Day last year.

Her testimony came after the athlete formally denied all of the charges against him in court today.

Pistorius' defence claim that he shot Ms Steenkamp through the toilet door because he mistook her for an intruder.

However, Ms Burger told the North Gauteng High Court in Pretoria that she heard a woman screaming before a series of shots were fired.

Pistorius passes Reeva Steenkamps mother as he enters the court [EPA]

Speaking through an interpreter, she said: "We woke up from the screams. My husband jumped up and went to the balcony.

"I was still sitting in the bed and I heard her screams."

She said she also heard a man screaming for help, adding: "Three times he yelled for help."

Ms Burger said she called security and expected them to call security at the neighbouring Silverwoods Estate.

She added: "I heard her screams again, it was worse, it was more intense.

"Just after her screams, I heard four shots, it was four gunshots that I heard."

Asked to describe the successive shots, she said there was a pause between the first and second which was longer between the second and third shots and the third and fourth.

She said: "I told my husband that I do not hope that that woman saw her husband being shot in front of her because after he screamed for help we didn't hear him again."

Ms Burger said it had been traumatic to hear the "bloodcurdling screams", adding: "It leaves you cold."

She said she and her husband later realised how important their evidence was when they saw they lived closer to Pistorius than other witnesses who had made statements.

Pistorius' trial for the murder of Reeva Steenkamp began today [AP]

Under cross-examination, Ms Burger described the screams as "fear-stricken" and "petrified", adding: "I could not understand how I could clearly hear a woman scream but Mr Pistorius couldn't hear that. I couldn't understand that."

She said the evening was confusing but also "distressing", telling the court: "The fear in that woman's voice is difficult to explain to the court."

Ms Burger continued: "It was a very emotional situation to have to hear. The absolute petrified screams and shouts, it was not just another evening, it was extremely emotional."

At one point, she offered to speak in English as she said some of her words were not being translated correctly from Afrikaans to English by the intepreter.

Asked to explain when the screams were in relation to the gunshots, she said: "I heard her screaming first, then I heard her call for help. Then I heard a man call for help three times.

"I then made a call, I gave the phone to my husband and he spoke to security. Afterwards I heard the woman's petrified screams again."

She said that she heard the woman screaming during the shots, and said the last time she heard her shout was just after the shots.

Ms Burger said: "I was convinced that that woman was being attacked, she and her husband were being attacked in their house. I was convinced it was an attack in the house by robbers. There was no doubt in my mind, because of the fear in that woman's voice.

"Because of the climax of her shouts I knew something terrible was happening in that house.

"You only shout like that if your life is really threatened."

Reality TV star Reeva was 29 when she died [AP]

Earlier, prosecutor Gerrie Nel had told the court that as there were no eyewitnesses to the killing "the state's case is based on circumstantial evidence."

He also denied separate charges under the Firearms Control Act, relating to firing a gun through the sunroof of a car in September 2012, and firing a gun whilst in a restaurant in Johannesburg in January last year, as well as possession of ammunition.

The court was read a statement from Pistorius in which he claimed he had mistakenly thought there was an intruder in his home, leading him to open fire in an attempt to protect himself and Miss Steenkamp.

The statement, read by Pistorius' defence lawyer while the athlete remained standing, said the scene had been contaminated and disturbed.

In it, the Paralympian said he did not intend to kill his then girlfriend that night and they had not argued that night.

He said: "I deny this allegation in the strongest terms because there was no argument. The allegation that I wanted to shoot (or kill) Reeva cannot be further from the truth."

June SteenKamp has said she wants to look her daughter's killer in the eyes [EPA]

Miss Steenkamp's mother June came face-to-face with the man accused of murdering her daughter for the first time today as she attended the trial.

She has previously said that she wants the chance to look Pistorius in the eyes.

Speaking to the Mail on Sunday, June Steenkamp said: “I want to look at Oscar, really look him in the eyes, and see for myself the truth about what he did to Reeva, and whatever the court decides at the end of his trial, I will be ready to forgive him.

“But first I want to force him to look at me, Reeva’s mother, and see the pain and anguish he has inflicted on me. I feel I need that.”

Today will be the first time the 67-year-old has met Pistorius, having only spoken to him once on the phone.

She said: "The only time I spoke to him was when Reeva phoned me from his car one day and pleaded with me to tell him to drive more slowly.

"I told her to give him the phone. I warned him that if he hurt my baby in any way I would wipe him out. He just kept saying, ‘OK, Mrs Steenkamp.’

"I know it sounds as if I was aggressive but I was desperate to keep Reeva safe. I couldn’t bear to think her life was in danger at his hands."

Reeva's parents June and Barry Steenkamp [ALAMY]

Prosecutors allege he was a weapons obsessive who deliberately killed his girlfriend in a fit of rage.

She was hit three times from the 9mm pistol - in the head, arm and hip and declared dead on the scene.

He has already admitted to culpable homicide, equivalent to manslaughter - a crime that could see him put away for 15 years.

The three-week trial at Pretoria High Court will arguably be the highest profile since the trial of American footballer OJ Simpson, who was cleared in 1995 of murdering his wife and a male friend.

A dedicated televison channel has been set up to provide live updates and much of the testimony from the proceedings can be broadcast.

There will be as many as 107 witnesses during the case of the trial in front of Judge Thokozile Masipa – juries were abolished by the apartheid government in the 1960s.